Revert of Adding task runner/ message loop to tests that use IsolateHolder.

Revert of Adding task runner/ message loop to tests that use IsolateHolder. (patchset #4 id:60001 of https://codereview.chromium.org/1130433002/)

Reason for revert:
speculative revert, gin unittests doesn't compile on mac builders anymore

Original issue's description:
> Adding task runner/ message loop to tests that use IsolateHolder.
>
> For adding v8 heap memory dump provider, the gin::IsolateHolder needs
> to have a task runner at initialization. The tests which don't
> initiallize task runner when initialization are changed in this CL to
> have either the message loop initializaed earlier or a dummy task
> runner. Refer crrev.com/1088683003 for the dump provider.
>
> BUG=476013
>
> Committed: https://crrev.com/54d19441b064ae06604c6a26c3863a091a8bb8bb
> Cr-Commit-Position: refs/heads/master@{#328531}

TBR=primiano@chromium.org,skyostil@chromium.org,ssid@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=476013
Committed: https://crrev.com/198cfb67ce30c38a2948c80628ce055fcb06a9ef
Cr-Commit-Position: refs/heads/master@{#328538}

[jochen (gone - plz use gerrit), 2015-05-06 15:09:06]

Created Revert of Adding task runner/ message loop to tests that use
IsolateHolder.

[commit-bot: I haz the power, 2015-05-06 15:09:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1129863002/1

[commit-bot: I haz the power, 2015-05-06 15:10:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-06 15:11:22]

Patchset 1 (id:??) landed as
https://crrev.com/198cfb67ce30c38a2948c80628ce055fcb06a9ef
Cr-Commit-Position: refs/heads/master@{#328538}